1. Field of the Invention
The present invention relates to a sensor for measuring a vibration, using a theory in which an induced current occurs when a conductor moves in a magnetic field, and more particularly, to a micromachined sensor for measuring a vibration, based on silicone micromachining technology in which a conductor is connected to masses moving due to a force caused by the vibration and the vibration is measured using induced electromotive power generated when the conductor moves in a magnetic field.
The present invention was partly supported by the IT R&D program of MIC/IITA [2006-S-054-02, titled: Development of CMOS based MEMS processed multi-functional sensor for ubiquitous environment]
2. Description of the Related Art
A micromachined sensor for measuring a vibration according to an exemplary embodiment of the present invention is one of sensors for a ubiquitous sensor network (USN). Particularly, in the case of a wireless sensor network, sensors are connected to one another via a wireless network and collect and monitor required environment information. Accordingly, such wireless sensor networks are generally, globally used.
As methods of mass-producing sensors that are essential elements for a wireless sensor network, recently, interests on micorelectromechanical system (MEMS) technology that is micromachining method using a semiconductor manufacturing process increase. The MEMS have advantages of mass production, subminiaturization, and low manufacturing costs since mechanical electronic devices manufactured by conventional mechanical processing may be collectively manufactured by a semiconductor process. Particularly, as conditions for sensors used in a wireless sensor network, low power, mass production, and low price are essential. Accordingly, MEMS type sensors may be most suitable.
As conventional sensors for measuring a vibration, there are used capacitance sensors, resonant frequency sensors, piezoelectric sensors, and piezoresistive sensors. However, in the case of such sensors have problems, it is required to electrically measure a capacitance and a frequency conversion, thereby complicating a signal processing method. Also, there are problems such as signal screen due to a parasitic capacitance and complexity of a device configuration. In addition, it is required to always generate a resonance by supplying power.
Problems of conventional technologies will be described as follows.
U.S. Pat. No. 4,805,456 discloses a resonant accelerometer in which a resonance frequency is differentiated, one mass is coupled with clamped-clamped beam type resonators opposite to each other interposing the mass therebetween, and the resonance frequency increasing and decreasing according to acceleration in an axis direction is used. In this case, compensation for a temperature is performed and the acceleration is differentiated. However, as defects, since the center of gravity of the mass is slanted to a bottom of a beam, the beam rotates due to the acceleration, thereby reducing a measuring area. Also, when the same beam is added on a bottom of a substrate to supplement this, tension of the beam becomes twice, thereby changing the resonant frequency and reducing sensitivity. Also, since the mass is separated from the beam, the resonance frequency is determined according to standards of the mass and the beam. When there is present a difference in the standards of the beams while manufacturing the same, the resonance frequency is changed. Also, since it is required to always supply power to the accelerometer, it is disadvantageous to be applied to wireless sensor network with low power.
U.S. Pat. No. 5,461,918 discloses a vibrating beam accelerometer capable of measuring magnitude of acceleration by measuring that a resonance frequency of a clamped-free vibrating cantilever, whose one end is fixed and another end is free, is changed by an external acceleration force. This technology is for removing a difficulty, in which a resonance frequency is determined according to standards of a mass and a vibrating beam, and provides a mass integrated with a vibrating beam. However, in this case, it is required to always supply power to the accelerometer that is a resonant type, which is disadvantageous to low power.
PCT/US90/00130 discloses a vibrating beam force transducer capable of measuring a resonance frequency changed by an external acceleration force while resonating as a phase of 180 degrees by using Lorentz's force generated when two conductive wires, through which currents flow opposite to each other, are present in a magnetic field. In this case, since it is required that the currents always flow, it is disadvantageous to low power consumption.